Eminem vs. Mariah Carey

He says they dated; she’s all, In your dreams! Then, after she allegedly impersonated him in a video for her song "Obsessed," he released a track with supposed details of their sex life and claimed to have proof of their fling. Shady!

Katherine Heigl vs. Isaiah Washington

After he denied hurling a gay slur at Grey’s Anatomy costar T.R. Knight, Heigl said, "he needs to just not speak in public" and added, ""T.R. is my best friend. I will throw down for that kid." Shortly after, Washington’s character was written off the show.

Courtney Love vs. Fred Durst

The Hole singer, who feels that feuding with her is a prerequisite for rock stars, said during a concert that the Limp Bizkit front man "brought about the worst years in rock history." Durst’s retort: "Courtney who?"

David Letterman vs. Sarah Palin

Mama Grizzly was none too amused when Letterman made a sexual joke about one of her daughters (not the underage one, he insisted; Palin didn’t buy it). She accepted his eventual mea culpa "on behalf of young women."

Rosie O’Donnell vs. Donald Trump

She accused him of using the 2006 Miss USA scandal for publicity; he fired off insults like "fat pig" and "degenerate." The school-yard showdown continued long after Barbara Walters warned them: Recess is over.